This isn't correct.
Sony were not doing what Amazon did.
Amazon just send you to Safari to buy from their web interface, they do not offer in-app purchases.
Sony built a store directly into the app, without using the Apple in-app purchasing system. This has always been disallowed, and is not connected to the changes related to subscription charges.

The point is that Apple has an iron fist around the store and its devices (make no mistake you do not OWN your iThing). Apple is in control. It can change any time they feel like it. If you are comfortable with that then go for it.